[llvm] [InstCombine] Handle `ICMP_EQ` when flooring by constant two (PR #73706)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

That was my concern too, but I couldn't find any instance that would violate this, so I believed restricting it `DivC == 2` was not necessary. Preconditions in the proof look correct to me.

https://github.com/llvm/llvm-project/pull/73706